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United States Patent |
5,046,366
|
Basson
,   et al.
|
September 10, 1991
|
Apparatus for measuring deflection or deformation in pavement structures
Abstract
A system 10 for measuring deflection and/or deformation of a layer in a
pavement structure under load is disclosed and claimed. The system
comprises at least one apparatus 11 including electric coils 17 sensitive
to relative movement between them and a separately anchored body 18 of
ferromagnetic material. The apparatus 11 comprises two longitudinally
spaced relatively moveable discs 19, 22 and a body 21 of a resilient,
transversely expandable material between the discs. A nut 25 serves to
urge the discs 19, 22 towards one another thereby causing the body 21
transversely to expand to secure the apparatus at a predetermined depth
against a wall in a test hole.
Inventors:
|
Basson; John E. B. (Pretoria, ZA);
Botha; Daniel F. (Pretoria, ZA);
Wijnberger; Otto J. (Pretoria, ZA)
|
Assignee:
|
CSIR (Pretoria, ZA)
|
Appl. No.:
|
489822 |
Filed:
|
March 9, 1990 |
Foreign Application Priority Data
Current U.S. Class: |
73/784 |
Intern'l Class: |
G01N 003/00 |
Field of Search: |
73/784,786
33/1 H,302,788,789,624,544-544.4
166/206-208
340/690
|
References Cited
U.S. Patent Documents
3380167 | Apr., 1968 | Abel, Jr. et al. | 33/1.
|
3419080 | Dec., 1968 | Lebourg | 166/207.
|
3538608 | Nov., 1970 | Bronson | 33/1.
|
3562916 | Feb., 1971 | Duckworth | 73/784.
|
4649741 | Mar., 1987 | Strom | 73/784.
|
4719803 | Jan., 1988 | Capelle et al. | 73/784.
|
Foreign Patent Documents |
0263626 | Apr., 1988 | EP.
| |
2042192 | Sep., 1980 | GB.
| |
2183845 | Jun., 1987 | GB.
| |
Other References
National Institute for Transport and Road Research etc.; "The Multi-Depth
Deflectometer: A Multistage Sensor, etc." Basson et al., Feb. 1981.
"The Multi-Depth Deflector, etc.", by Morris de Beer et al. Paper accepted
for the first International Symposium on nondestructive testing, etc.
"Effective Moduli and Stress Dependence of Payment Materials as Measured in
Some Heavy-Vehicle Simulator Tests" by J. H. Maree et al.
"Field Evaluation of the Multi-Depth Deflectometers"--Search Report 1123-2
by T. Scullion et al., Report date Sep. 1988.
"Use of Multidepth Deflector for Deflection Measurements" by Tom Scullion
and A. J. Bush.
"Using the Multidepth Deflectomer to Verify Modulus Backcalculation
Procedures" by Tom Scullion et al.
|
Primary Examiner: Raevis; Robert
Attorney, Agent or Firm: Nixon & Vanderhye
Claims
We claim:
1. A system for measuring deflection and/or deformation of a layer in a
pavement structure under load comprising:
apparatus comprising electronic means sensitive to relative movement
between itself and a separately anchored member;
the apparatus also comprising means for securing the electronic sensitive
means in a hole in the structure in a region close to the layer;
the securing means being connected to the electronic sensitive means and
comprising two longitudinally spaced, relatively moveable circular
disc-like members and a circular cylindrical body of a resilient,
transversely expandable material sandwiched between the spaced members;
the apparatus further comprising means actuable to urge the two members
towards one another causing the body transversely to expand beyond the
peripheries of the disc-like members thereby to secure the electronic
sensitive means against a wall of the hole;
the disc-like members and circular cylindrical body defining at least one
longitudinally extending peripheral slot;
the apparatus also comprising ducting for electric wiring extending from
the electronic sensitive means, the ducting being located in the
peripheral slot to extend from the electronic sensitive means to the
disc-like member furthest away from the electronic sensitive means; and
the separately anchored member, in use, being anchored in the structure in
a region thereof that does not deflect under the load so that relative
movement between the stationary separately anchored member and the
electronic sensitive means secured to the layer may be measured.
2. A system as claimed in claim 1 wherein the electronic sensitive means is
covered with a protective jacket, wherein the disc-like members and jacket
are of substantially equal diameter and wherein the jacket also defines a
longitudinal peripheral slot for the ducting.
3. A system as claimed in claim 2 wherein the disc-like members, resilient
body and jacket define two diametrially opposed slots wherein two opposed
ducts are mounted; and wherein outer surfaces of the ducts are
substantially flush with the peripheries of the disc-like members.
4. A system as claimed in claim 1 wherein the electronic sensitive means
comprises coils of a linear variable differential transformer and the
separately anchored member comprises a body of a ferromagnetic material.
5. A system as claimed in claim 4 wherein the coils are located in an
elongate bored housing; wherein the two disc-like members and resilient
body define holes and a bore, respectively registering with the bore of
the housing and wherein the body of ferromagnetic material, in use, is
carried on a rod extending through the registering bores so that the body
of ferromagnetic material is positioned in the bore of the housing in the
region of the coils.
6. A system as claimed in claim 5 wherein a first of the disc-like members
is mounted on the housing for the coils, wherein a hollow threaded stem is
secured to the first disc-like member, the stem communicating with the
hole in the first member and extending through the bore defined in the
resilient body and the hole in the second disc-like member; and wherein
the means actuable to urge the two disc-like members towards one another
comprises a nut co-operating with the thread on the stem.
7. A system as claimed in claim 6 wherein the nut defines two diametrically
opposed radially extending slots and wherein the system comprises a tool
for gripping the apparatus and for actuating the nut, the tool comprising
an inner elongate rotatable member comprising two diametrically opposed
projections at one end thereof adapted to be received in the slots in the
nut and means towards the other end thereof for rotating the member; a
coaxial outer sleeve moveable on the inner member in telescopic fashion;
and jaws mounted between the inner member and outer sleeve actuable by
longitudinal movement of the outer sleeve to open and close, thereby to
release or grip the apparatus.
8. A system as claimed in claim 1 wherein the resilient body is glued to
the two disc-like members.
9. A system as claimed in claim 5 comprising an anchor for anchoring the
rod in the bottom of the hole, the anchor comprising an elongate leading
portion having transversely extending projections thereon, a tail portion
and a yieldable bellows member co-axially mounted on the anchor to protect
the tail portion against matter that may fall into the hole, thereby to
prevent disturbance of the anchor.
10. A system as claimed in claim 1 comprising a top cap assembly for
closing the hole, the top cap assembly comprising a cup mountable in the
hole at the mouth thereof, and apparatus including means sensitive to
relative movement between itself and a separately anchored member
mountable in or on the cup and a lid for the cup.
Description
This invention relates to road or pavement engineering and more
particularly to apparatus for and a method of measuring transient
deflection and permanent deformation of different layers in a pavement
structure.
With the availability of the so-called Heavy Vehicle Simulator it has
become possible to simulate many years of trafficing on a test section of
pavement structure over a relatively short period of two to three months.
The pavement's response to this simulated trafficing was initially
monitored by measuring total surface deflection, radius of curvature and
permanent deformation. The interpretation of these measurements proved
difficult in multi-layered pavement structures as more detailed
information is required on the response of each layer in the structure.
In a prior published document there is disclosed a system wherein apparatus
comprising means sensitive to relative movement between itself and a
separately anchored member is secured to a wall of a test hole by means of
an assembly comprising a circular member having a conical surface, a
spaced circular member having a planar surface, a plurality of steel balls
between the two members and a peripheral elastic sleeve between the
members. By urging the two members towards one another, the balls are
urged radially outwardly to bear against the wall of the hole, thereby to
suspend the apparatus in the hole.
The main disadvantage of this system is that the contact made with the wall
of the hole is not continuous along the whole of the periphery of the
assembly, but rather a plurality of point contacts where each ball bears
against the wall. This may result in the apparatus becoming misaligned in
the hole, especially if only one or more adjacent balls bear against a
hard object in the wall. Furthermore, the aforementioned apparatus is
expensive and difficult to manufacture.
It is an object of the present invention to provide an improved system for
measuring the response of various vertically spaced layers in a pavement
structure under load.
According to the invention a system for measuring deflection and/or
deformation of a layer in a pavement structure under load comprises:
apparatus comprising electronic means sensitive to relative movement
between itself and a separately anchored member;
the apparatus also comprising means for securing the sensitive means in a
hole in the structure in a region close to the layer;
the securing means being connected to the sensitive means and comprising
two longitudinally spaced, relatively moveable circular disc-like members
and a circular cylindrical body of a resilient, transversely expandable
material sandwiched between the spaced members;
the apparatus further comprising means actuable to urge the two members
towards one another causing the body transversely to expand beyond the
peripheries of the disc-like members thereby to secure the sensitive means
against a wall of the hole;
the disc-like members and circular cylindrical body defining at least one
longitudinally extending peripheral slot;
the apparatus also comprising ducting for electric wiring extending from
the sensitive means, the ducting being located in the peripheral slot to
extend from the sensitive means to the disc-like member furthest away from
the sensitive means; and
the separate member, in use, being anchored in the structure in a region
thereof that does not deflect under the load so that relative movement
between the stationary separate member and the sensitive means secured to
the layer may be measured.
It will be appreciated that with the body of ferromagnetic material
associated with the apparatus anchored in the hole to limit movement
thereof transversely to the surface of the pavement during use, the
sensitive means, which is secured to a layer as hereabove defined, will
give an indication of the deflection of the layer under load, relative to
the anchor and also of any permanent deformation of such layer.
Furthermore, a plurality of the apparati according to the invention may be
secured in the hole spaced above one another and to different layers in
the pavement to provide deflection and/or deformation indications of each
of these layers.
The sensitive means may be covered with a protective jacket, the disc-like
member and jacket may be of substantially equal diameter and the jacket
may also define a longitudinal peripheral slot for the ducting.
The disc-like members, resilient body and jacket may define two
diametrially opposed slots wherein two opposed ducts may be mounted so
that the outer surfaces of the ducts are substantially flush with the
peripheries of the disc-like members.
The sensitive means preferably comprises coils of a linear variable
differential transformer and the separate member preferably comprises a
body of a ferromagnetic material.
The coils are preferably located in an elongate bored housing; the two
disc-like members and resilient body define holes and a bore, respectively
registering with the bore of the housing and the body of ferromagnetic
material, in use, is carried on a rod extending through the registering
bores so that the body of ferromagnetic material is positioned in the bore
of the housing in the region of the coils.
A first of the disc-like members may be mounted on the housing for the
coils, a hollow threaded stem may be secured to the first disc-like member
with the stem communicating with the hole in the first member and
extending through the bore defined in the resilient body and the hole in
the second disc-like member; and the actuating means may comprise a nut
co-operating with the thread on the stem.
The resilient body is preferably glued to the two disc-like members.
The nut preferably defines two diametrically opposed radially extending
slots and the system may comprise a tool for gripping the apparatus and
for actuating the nut. The tool may comprise an inner elongate rotatable
member comprising two diametrically opposed projections at one end thereof
adapted to be received in the slots in the nut and means for rotating the
member towards the other end thereof; a coaxial outer sleeve moveable on
the inner member in telescopic fashion; and jaws mounted between the inner
member and outer sleeve actuable by longitudinal movement of the outer
sleeve to open and close, thereby to release or grip the apparatus.
The system may also comprise anchor for anchoring the rod in the bottom of
the hole, the anchor comprising an elongate leading portion having
transversely extending projections thereon, a tail portion and a yieldable
bellows member co-axially mounted on the anchor to protect the tail
portion against matter that may fall into the hole, thereby to prevent
disturbance of the anchor.
The system may further comprise a top cap assembly for closing the hole,
the top cap assembly comprising a cup mountable in the hole at the mouth
thereof, and apparatus including means sensitive to relative movement
between itself and a separately anchored member mountable in or on the cup
and a lid for the cup.
The invention will now further be described, by way of example only, with
reference to the accompanying diagrams wherein:
FIG. 1: is a diagrammatic side elevation of a system for measuring the
deflection and/or deformation of a plurality of layers in a pavement
structure under load, mounted in a test hole drilled in the pavement
structure;
FIG. 2: is an exploded perspective view of apparatus for measuring the
deflection and/or deformation of a layer in the structure under load;
FIG. 3: is a perspective view of the apparatus of FIG. 2 fully assembled
and also showing an installation tool for securing the apparatus at a
predetermined level in the test hole;
FIG. 4: is a diagrammatic view of an anchor for a rod carrying bodies of
ferromagnetic material associated with the apparati for measuring the
deflection and/or deformation;
FIGS. 5 to 7: are various views of a connection between the rod and the
anchor;
FIG. 8: is a diagrammatic perspective view of an alternative top cap
assembly for the test hole including apparatus for measuring the
deflection and/or deformation of a region of the structure close to the
surface thereof; and
FIG. 9: is a diagrammatic side elevation of the top cap assembly mounted in
the hole to close the hole.
A system for measuring the deflection and/or deformation of a plurality of
layers at different levels in a pavement structure under load, is
generally designated by the reference numeral 10 in FIG. 1.
The system 10 comprises two (or any other suitable number) apparati 11 for
measuring the deflection and/or deformation of layers 12 and 13,
respectively in the structure, mounted at different, predetermined levels
in a test hole 14.
Hole 14 is 35 to 40 mm in diameter and is lined with a neoprene sleeve 15.
Sleeve 15 serves to ensure stability of both the hole and the system 10
during accelerated testing by means of a Heavy Vehicle Simulator (not
shown). The Heavy Vehicle Simulator is a structure with which many years
of trafficing over a test section of the pavement structure may be
simulated over a relatively short period of two to three months.
Apparati 11 are secured to the inner wall of the hole 14 as will be
described herebelow.
As best shown in FIG. 2, each apparatus 11 comprises a linear variable
differential transformer (LVDT) comprising a bored circular cylindrical
housing 16 for transformer coils 17 sensitive to movement of a separate
body of ferromagnetic material 18 relative thereto.
The E-series LVDT's sold by SHAEVITZ ENGINEERING have been found to be
suitable for the purposes of the invention. As will be described
herebelow, the body 18, in use, is anchored in the hole 14 so that it is
positioned in the bore of housing 16. Housing 16 is enclosed in an epoxy
jacket 16.1, defining two diametrically opposed slots 16.2.
A first disc like member 19 defining a centre hole (not shown) and
supporting a hollow threaded stem 20 communicating with the hole is
mounted on one end of the housing 16. A circular cylindrical body 21 of a
resilient, transversely expandable material, such as silicon rubber, is
located between and glued to the first disc 19 and a second similar disc
22. The stem 20 passes through a bore 23 defined in the body 21 and a hole
24 defined in the second disc 22.
A threaded nut 25 serves to co-operate with the thread on the stem 20 to
urge second disc 22 towards or away from first disc 19, thereby to cause
the body 21 transversely to expand or to return to its normal
configuration. When the nut 25 is tightened, body 21 is caused to expand
thereby to secure and suspend the apparatus 11 in hole 14. With the
resilient body 21 of the present invention, there is a continuous contact
area between the apparatus 11 and the wall and the forces suspending the
apparatus 11 in the hole are substantially uniform along the whole of the
periphery of body 21. Nut 25 defines diametrically opposed peripheral
slots 26 adapted to co-operate with complementary formations 37 (shown in
FIG. 3) on an installation tool 32 as will be described herebelow.
Diametrically opposed and longitudinally extending ducts 27 for electrical
wiring 28 connected to the coils 17 in housing 16 are also provided on
apparatus 11. Ducts 27 are located in diametrically opposed peripheral
slots 29 to 31 defined in disc 19, collar 21 and disc 22 respectively and
in slots 16.2 of epoxy jacket 16.1.
Apparati 11 are located and secured in hole 14 by means of installation
tool 32 shown in FIG. 3. Tool 32 comprises an inner elongate rotatable
member 33. An outer sleeve 34 is co-axially mounted on inner member 33 and
is moveable in telescopic fashion in a longitudinal direction relative to
inner member 33. Jaws 35 are mounted between sleeve 34 and member 33 to
project beyond one end thereof and to be moveable transversely inwardly
and outwardly relative to member 33 upon telescopic manipulation of sleeve
34. The outer surfaces of jaws 35 are sloped and gripping formations 36
are provided on the inner surfaces. Formations 37 on the one end of member
33 are adapted to co-operate with slots 26 on nut 25 of apparatus 11. A
tommy bar 38 is provided towards the other end of member 33 to enable
rotation of the latter relative to sleeve 34.
In use, sleeve 34 is moved away from the one end of member 33 thereby to
cause jaws 35 to move outwardly toward their normal rest position.
Apparatus 10 is then positioned between jaws 35 with formations 37
received in slots 26. Sleeve 34 is moved towards the one end of member 33
to close the jaws and to grip the apparatus between jaws 35.
The apparatus is then positioned at the desired level in hole 14, nut 25 is
tightened by rotating inner member 33 by means of tommy bar 38. Expandable
body 21 is caused transversely to expand and to secure apparatus 11 in a
suspended condition in hole 14.
Referring again to FIG. 1, the bodies 18 of apparati 11 are supported in
the hole 14 by an anchor 40. As best shown in FIG. 4 anchor 40 comprises
an enlongate member having a sharpened leading portion 41 with
transversely projecting formations 42 thereon and a tail 44. A yieldable
bellows-like sleeve 43, coaxially mounted on the elongate member, protects
the regions of tail 44 covered thereby against matter that may fall into
the hole to prevent the anchor from being disturbed.
A socket defining member 45 of a connector 46 shown in FIGS. 5 to 7 is
connected to tail 44 of anchor 40. A male member adapted to fit into
socket 47 in snap fit fashion is designated by the reference numeral 48.
This member is provided at the one or bottom end of a rod 49 for carrying
bodies 18 at selected positions along its length as best shown in FIG. 1.
It will be appreciated that with the bodies 18 supported by rod 49 which is
anchored by anchor 40 at a level approximately two meters below the
surface of the pavement, where little or no deflection under load is
expected, the apparati 11, suspended between the walls of the hole, may
move relative to the bodies 18 under the influence of a load.
The LVDT's are adapted to sense this relative movement and to transmit
information relating to any deflection or deformation via wiring 28 to
recording apparatus (not shown) above the surface of the pavement.
A top cap assembly carrying a LVDT, such as those referred to hereabove, is
designated generally by the reference numeral 50 in FIGS. 8 and 9. This
top cap assembly is different from the top cap shown in FIG. 1 and is
intended to measure deflections and/or deformations close to the surface
51 of the pavement.
The top cap assembly comprises a cup 52 defining a hole 53 circumscribed by
a flange 54. A sleeve 55 with a flange (not shown) extends through hole 53
with the flange abutting against flange 54 of the cup 52 on the inside
thereof.
A coil carrying housing 56 of the aforementioned LVDT and which defines a
bore 57 is secured to a suspending member in the form of a disc 58 adapted
to fit into cup 52 and to abut against the flange of the sleeve 55. Disc
58 defines a plurality of holes and slots 59 through which the wiring 28
of all the apparati 11 in the hole pass to the aforementioned recording
apparatus. Anchored rod 49 carries a body 62 of ferromagnetic material
associated with the LVDT of the top cap assembly toward at its upper end
so that the body 62 extends into bore 57 of housing 56 and is thus
anchored separately from the coil carrying housing 56.
A lid 60 mountable on cup 52 closes off the hole 14 and should be flush
with the top surface 51 of the pavement.
The system of FIG. 1 is installed as follows.
First the hole 14 is drilled. The depth of the hole may vary between a few
centimeters and four meters and the diameter is in the order of 35-39 mm.
The top part of the pavement structure (also shown in FIG. 9) is cut to
have a diameter of 90 mm by 22 mm deep. The cup portion 52 of the top cap
assembly, either that shown in FIG. 1 or the assembly 50 of FIGS. 8 and 9,
is located in this region by embedding it in a polyurethane bedding
compound 61. In yet other embodiments, the cup assembly may in situ be
cast from polyurethane.
Next the leading portion 41 of anchor 40 is secured in the bottom of the
hole 14 with a mixture of cement and coarse river sand. A pre-formed
neoprene tube, which will form lining 15, is inserted by means of a metal
tube covered with a suitable anti-bonding agent, such as silicon grease. A
polyurethane compound is then poured into the annular region between the
neoprene tube and the walls of hole 14. The mixture is then allowed to set
and the metal tube withdrawn from the hole.
The socket portion 45 of connector 46 is next secured to anchor 40. A pilot
rod (not shown) is then fitted into socket 47. This rod serves to guide
the apparati 11 into their selected positions.
Starting with the apparatus 11 to be mounted deepest in the hole these
apparati are secured, one after the other, at selected levels to the walls
of hole 14 by means of tool 32, as hereabove described.
As shown in FIG. 1, the apparati 11 are connected via wiring 28 passing
through the ducts 27 of apparati higher up in the hole to the
aforementioned recording apparatus.
A dummy rod (also not shown) carrying a body of ferromagnetic material is
passed through the registering stems 20 and bores of the housings 16 and
is used to test each of the apparati. This rod is also used to measure the
exact depth of each apparatus 11 below the surface. These measurements are
used in assembling rod 49 for carrying bodies 18 at the measured intervals
along its length.
The assembled rod 49 is then passed through the aforementioned registering
stems and bores in apparati 11 and snapped into socket 47. The
ferromagnetic body 18 of each LVDT is positioned in the bore of housing 16
of that LVDT. After calibration and final inspection of the arrangement,
the hole 14 is closed by means of lid 60.
With the apparatus 11 and the system 10 according to the invention, it is
possible to measure the deflections, changes in deflection, permanent
deformation and changes in permanent deformation of the different layers
in a pavement structure. From the deflections of the various layers it is
also possible to back calculate the "effective" elastic moduli of the
various layers. The term "effective" is used to distinguish the elastic
moduli measured in the laboratory from those determined indirectly with
the system 10 according to the invention. The back calculation is
performed by using a multi-layered linear elastic computer programme where
the user repeatedly changes the moduli of the layers until a depth
deflection curve similar to that measured with the system is found.
Usually an acceptable fit is achieved when the deviation from each
deflection measurement is less than 0,0015 mm.
It will be appreciated that there are many variations in detail possible on
the invention herein disclosed without departing from the scope and spirit
of the appended claims
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